I Wanna Be The Adazel

Like in I Wanna Be The Diverse, theres one boss that is fought one time, another with help from another boss and is possessed by the ghosts of the previous bosses making him/her the final boss. This prime example is Adazel. Adazel has his own boss music for each fight. This particular music is the boss theme that plays when you fight Kraid: https://www.youtube.com/watch?v=-pRWx5AUKLQ. And his final fight music is the music when you enter the Haunted Playground: https://www.youtube.com/watch?v=ZdPx8pQfqSs